This invention generally relates to a particular phosphor which is intended to be used in fluorescent lamps and, more particularly, to a method for treating the phosphor so that the performance of the fluorescent lamp which incorporates this phosphor will be improved.
Strontium chloroapatite activated by divalent europium is now a commercial luminescent material and is described in detail in copending application Ser. No. 726,464, filed May 3, 1968, and owned by the present assignee. Such a luminescent material is a very efficient blue-emitting phosphor and is particularly useful as a component in phosphor blends and for special applications such as the treatment of infantile hyperbilirubinemia. The use of this phosphor in the latter application is described in U.S. Pat. No. 3,658,068 dated Apr. 25, 1972.
When the foregoing strontium chloroapatite phosphor is incorporated in fluorescent lamps as a coating on the inner surface of the lamp envelope, the performance of the resulting lamp is quite variable. More specifically, the output of the lamps after they have been operated for 100 hours is apt to diminish considerably and the luminosity can drop as much as 25% during the first 100 hours of operation. In some cases this drop in luminosity is not as severe, but as a general rule, this excessive drop in luminosity will be manifested during the first 100 hours of operation. This has limited the use of fluorescent lamps which incorporate this phosphor.